Radar systems can be used to track objects. However, the resolution with which a radar system can track an object is limited to the size of the object, that is to say, radar systems cannot track an object to a resolution which is finer than the size of the object.
One technique for improving the resolution of radar tracking is to place a radar target, called a responder, on the tracked object. A device accurately measures the range and bearing to the responder to calculate the relative position and heading of the object relative to the device. Using a responder improves the resolution with which the object can be tracked.
Radar tracking using responders is often used in a marine environment, for example, on offshore oil-platforms where a responder is placed on the oil-platform and a device on a vessel monitors the responder on the oil-platform to allow the vessel to maintain a safe distance from the oil-platform. Responders are also used in pipe or cable laying operations where convoys of vessels involved in the pipe or cable laying follow one another, for example, a supply ship containing a supply of pipes has a device which monitors a responder on a pipe laying vessel to ensure that the pipe laying vessel and the supply ship remain in convoy, so that the pipe laying vessel can reliably use a crane to pick the pipes up from the supply ship.
A disadvantage with using responders is that a responder must be fitted to every vessel that might be tracked at some point in the future. This requires that the desire to track the vessel is predicted in advance so that a responder can be fitted. Inevitably this will mean that some vessels that one wishes to track will not have a responder fitted, or might have a responder from a different manufacturer fitted which is not compatible with the device, leading to delays while an appropriate responder is fitted. In other cases, vessels may have a responder fitted but never be tracked which wastes time and money involved in fitting an unused responder.
It would, therefore, be advantageous to find a way of tracking an object to high resolution without the need to use a responder.